"They saw this woman push another woman and they flagged down two police officers," NYPD Chief of Manhattan South Detectives William Aubry told the CBS New York after horrified witnesses pointed out Liverpool. "It’s a horrible incident and your heart goes out to this family and this victim."

After interrogating Liverpool, investigators have taken a second look at a similar death in another subway station on October 19 that was originally ruled a suicide.

Police said Liverpool admitted to pushing the woman, whom she reportedly did not know, while under interrogation.

Liverpool has a history of mental illness, police said.

Read: Man Who Took Selfies With Mom's Severed Head After Killing Her Is Found Guilty of Her Murder

However, at her arraignment on a 2nd degree murder charge Tuesday, Liverpool pleaded not guilty. "I didn’t admit to nothing," she said at the hearing.

The October 19 victim was a 27-year-old woman, according to reports following the incident. An MTA spokesperson at the time said the woman was seen jumping onto the tracks.